1. Field of the Invention
This invention relates to a servo-type capsule-equipped instrument that can be utilized conveniently as an altimeter of an aircraft. More specifically, it relates to a servo-type capsule-equipped instrument having an error correcting mechanism, which is improved so as to remove errors arising from the inherent properties of the capsule and obtain a highly accurate display or output.
2. Description of the Prior Art
There are widely used capsule-equipped instruments which are adapted to indicate on an enlarged scale an axial deformation of the capsule which is caused by a difference in pressure between the inside and outside of the capsule.
An altimeter of the simplest structure is constructed so as to convert the axial change of the capsule into a change in the rotating direction, then enlarge this change and indicate it by a pointer.
In displaying, the deflecting angle of the pointer is desirably proportional to the altitude. To achieve this, efforts have long been directed to improvement of the properties of the capsule and the characteristics of the angle conversion device. Since, however, it is difficult to obtain capsule having ideal properties for an equiangular display of altitude and the properties vary from capsule to capsule, the actual situation is that errors corresponding to the altitude are allowed in the display.
FIG. 1 of the accompanying drawings is a graph showing the allowable range of display errors and one example of the characteristics of a conventional altimeter. In FIG. 1, the polygonal line a shows the allowable positive upper limit; the polygonal line b, the allowable lower limit; and the polygonal line c, one example of the characteristics of the conventional altimeter.
Instrument manufacturers are trying to obtain altimeters of high accuracy by selecting a capsule and adjusting the coupling between it and a converter. In the example shown in FIG. 1, a relatively correct display is obtained in a low altitude region and in the vicinity of 9,114 meters (30,000 feet), but considerable errors, although within the allowable limits, remain in the vicinity of 6,096 meters (20,000 feet) and in the vicinity of 120,192 meters (40,000 feet).
It is extremely difficult to reduce such errors by improving the properties of the capsule.
Such errors should desirably be minimized when the altimeter is to be operated by servomechanisms to feed information to an automatic pilot of an aircraft.